Re: casefile random access

[Ben Pfaff]

John Darrington <address@hidden> writes:

> If you're able and willing to write a random access casereader, then
> that will certainly make the gui code simpler.  I've got a change
> almost ready to commit, which will remove the GUI's hard limit  on the
> number of variables.   The next major step for the GUI is to unlimit
> the number of cases. So I'm just about ready to use such casereader.
>
>
> My idea of the interface would be something along the lines of the
> following, but you may have better ideas.

Here's an implementation with a different interface.  If you like
it, I'll check it in.  Let me know.

Index: src/data/casefile.h
===================================================================
RCS file: /cvsroot/pspp/pspp/src/data/casefile.h,v
retrieving revision 1.2
diff -u -p -r1.2 casefile.h
--- src/data/casefile.h 10 May 2006 04:08:25 -0000      1.2
+++ src/data/casefile.h 6 Jun 2006 00:36:41 -0000
@@ -44,12 +44,15 @@ bool casefile_append_xfer (struct casefi
 void casefile_mode_reader (struct casefile *);
 struct casereader *casefile_get_reader (const struct casefile *);
 struct casereader *casefile_get_destructive_reader (struct casefile *);
+struct casereader *casefile_get_random_reader (const struct casefile *);
 
 const struct casefile *casereader_get_casefile (const struct casereader *);
 bool casereader_read (struct casereader *, struct ccase *);
 bool casereader_read_xfer (struct casereader *, struct ccase *);
 void casereader_destroy (struct casereader *);
 
+void casereader_seek (struct casereader *, unsigned long case_idx);
+
 unsigned long casereader_cnum(const struct casereader *);
 
 #endif /* casefile.h */
Index: src/data/casefile.c
===================================================================
RCS file: /cvsroot/pspp/pspp/src/data/casefile.c,v
retrieving revision 1.9
diff -u -p -r1.9 casefile.c
--- src/data/casefile.c 10 May 2006 04:08:25 -0000      1.9
+++ src/data/casefile.c 6 Jun 2006 00:36:41 -0000
@@ -150,6 +150,7 @@ struct casereader 
     struct casefile *cf;                /* Our casefile. */
     unsigned long case_idx;             /* Case number of current case. */
     bool destructive;                   /* Is this a destructive reader? */
+    bool random;                        /* Is this a random reader? */
 
     /* Disk storage. */
     int fd;                             /* File descriptor. */
@@ -174,10 +175,11 @@ static size_t case_bytes;
 static void register_atexit (void);
 static void exit_handler (void);
 
-static void reader_open_file (struct casereader *reader);
-static void write_case_to_disk (struct casefile *cf, const struct ccase *c);
-static void flush_buffer (struct casefile *cf);
-static bool fill_buffer (struct casereader *reader);
+static void reader_open_file (struct casereader *);
+static void write_case_to_disk (struct casefile *, const struct ccase *);
+static void flush_buffer (struct casefile *);
+static void seek_and_fill_buffer (struct casereader *);
+static bool fill_buffer (struct casereader *);
 
 static void io_error (struct casefile *, const char *, ...)
      PRINTF_FORMAT (2, 3);
@@ -530,6 +532,17 @@ casefile_get_reader (const struct casefi
   return reader;
 }
 
+/* Creates and returns a random casereader for CF.  A random
+   casereader can be used to randomly read the cases in a
+   casefile. */
+struct casereader *
+casefile_get_random_reader (const struct casefile *cf) 
+{
+  struct casereader *reader = casefile_get_reader (cf);
+  reader->random = true;
+  return reader;
+}
+
 /* Creates and returns a destructive casereader for CF.  Like a
    normal casereader, a destructive casereader sequentially reads
    the cases in a casefile.  Unlike a normal casereader, a
@@ -556,8 +569,6 @@ static void
 reader_open_file (struct casereader *reader) 
 {
   struct casefile *cf = reader->cf;
-  off_t file_ofs;
-
   if (!cf->ok || reader->case_idx >= cf->case_cnt)
     return;
 
@@ -585,6 +596,19 @@ reader_open_file (struct casereader *rea
       memset (reader->buffer, 0, cf->buffer_size * sizeof *cf->buffer); 
     }
 
+  case_create (&reader->c, cf->value_cnt);
+
+  seek_and_fill_buffer (reader);
+}
+
+/* Seeks the backing file for READER to the proper position and
+   refreshes the buffer contents. */
+static void
+seek_and_fill_buffer (struct casereader *reader) 
+{
+  struct casefile *cf = reader->cf;
+  off_t file_ofs;
+
   if (cf->value_cnt != 0) 
     {
       size_t buffer_case_cnt = cf->buffer_size / cf->value_cnt;
@@ -601,8 +625,6 @@ reader_open_file (struct casereader *rea
 
   if (cf->case_cnt > 0 && cf->value_cnt > 0)
     fill_buffer (reader);
-
-  case_create (&reader->c, cf->value_cnt);
 }
 
 /* Fills READER's buffer by reading a block from disk. */
@@ -696,6 +718,21 @@ casereader_read_xfer (struct casereader 
     }
 }
 
+/* Sets the next case to be read by READER to CASE_IDX,
+   which must be less than the number of cases in the casefile.
+   Allowed only for random readers. */
+void
+casereader_seek (struct casereader *reader, unsigned long case_idx) 
+{
+  assert (reader != NULL);
+  assert (reader->random);
+  assert (case_idx < reader->cf->case_cnt);
+
+  reader->case_idx = case_idx;
+  if (reader->cf->storage == DISK)
+    seek_and_fill_buffer (reader);
+}
+
 /* Destroys READER. */
 void
 casereader_destroy (struct casereader *reader)
Index: src/language/tests/casefile-test.c
===================================================================
RCS file: /cvsroot/pspp/pspp/src/language/tests/casefile-test.c,v
retrieving revision 1.2
diff -u -p -r1.2 casefile-test.c
--- src/language/tests/casefile-test.c  15 Mar 2006 03:29:11 -0000      1.2
+++ src/language/tests/casefile-test.c  6 Jun 2006 00:36:41 -0000
@@ -21,11 +21,14 @@
 #include <data/casefile.h>
 #include <data/case.h>
 
+#include <gsl/gsl_randist.h>
 #include <gsl/gsl_rng.h>
 #include <stdarg.h>
 #include <language/command.h>
 #include <language/lexer/lexer.h>
 
+#include "xalloc.h"
+
 static void test_casefile (int pattern, size_t value_cnt, size_t case_cnt);
 static void get_random_case (struct ccase *, size_t value_cnt,
                              size_t case_idx);
@@ -133,6 +136,24 @@ test_casefile (int pattern, size_t value
     casereader_destroy (r1);
   if (pattern != 2)
     casereader_destroy (r2);
+  if (pattern > 3) 
+    {
+      int *order;
+      r1 = casefile_get_random_reader (cf);
+      order = xmalloc (sizeof *order * case_cnt);
+      for (i = 0; i < case_cnt; i++)
+        order[i] = i;
+      if (case_cnt > 0)
+        gsl_ran_shuffle (rng, order, case_cnt, sizeof *order);
+      for (i = 0; i < case_cnt; i++)
+        {
+          int case_idx = order[i];
+          casereader_seek (r1, case_idx);
+          read_and_verify_random_case (cf, r1, case_idx);
+        }
+      casereader_destroy (r1);
+      free (order);
+    }
   if (pattern > 2) 
     {
       r1 = casefile_get_destructive_reader (cf);

-- 
"J'avais trouv'e ma religion :
 rien ne me parut plus important qu'un livre.
 La biblioth`eque, j'y voyais un temple."
--Jean-Paul Sartre